Research On Detection Of Radio Wave Penetration For Small Geological Structure In Coal Face

The mining of fully mechanized coal face has got more extensive use.It is more significant for coal mining safety to further enhance the cognition of the distributing state and the development degree and the precise location of the geological structures within coal face.Radio-wave penetration method is characterized by its high work efficiency,long perspective distance and low cost,so it is a preferred surveying method for exploring geological anomaly bodies within the coalface.In addition to practical data,this paper has carried out systematic research from observation system,simulation experiment and data processing technology.This paper has carried out the radio wave ground experiment based on the small receiving space.The result of experiment from four roadway observation system is more exact than that of two roadway observation system,which is good for exact detection of small geological structure.On the basis of detection data of radio-wave penetration and geologic data decolsed by mining,the research has been carried out from imaging techniques,parameter setting,the result as follows:(1)The inversion methods of ART,SIRT,LSQR,give their results of absorption coefficient values in each grid cell within coal face,which all can reflect the major geological anomalies with throw greater than one half coal thickness.The geological anomalies with throw less than one half coal thickness can also be reflected in the results to a certain degree.The SIRT inversion result has a better agreement compared with the other two inversion results.(2)The results from such inversion maps as the distribution map of measured field intensity,the distribution map of difference of field intensity,the distribution map of ratio of field intensity,are similar as whole to interpret geological structure,All of them can well control the vertical scope of geological anomalies with throw greater than one half coal thickness,but not so well for the geological anomalies with throw less than one half coal thickness,and no obvious reflection for the geological anomalies with throw less one third coal thickness.The distribution map of measured field intensity could reflect the change of measured field intensity value in the coal workface,and show better reflection of geological abnormity degree than those of the others.(3)Through the comparison analysis of SIRT inversion by setting up various grid sizes,when the unit grid size shares the same scale with the actual receiving space,the SIRT inversion will get the best reflection of the geological anomalies.(4)The radio-wave penetration with 5m-receiving space can acquire more reliable measured data than with lOm-receiving space,so its result can more effectively control distance of the boundary of geological anomalies.Especially for the small-area geological anomalies,by applying receiving space of 5m instead of 10m,the number of data of abnormal field intensity will be doubled,which means that the acquiring abnormity zones is more reliable.(5)On the condition that the other inversion parameters ramain unchanged,with the increase of iteration time within 50 times,the reflection of geological anomalies from SIRT inversion result is more reliable and sensitive.However,the iteration inversion result will not change when more than 50 iteration times.Thus,the number of max iteration times should be chosen more than 50 times.